you guys are just awesome
had a look at an older save, that rail segment was supposed to have Unit Number: 13958858 originaly. Hope I won't find a way to reproduce though :')

We're running a moderatley modded SpaceExploration playthrough (hosting the saved game directly from steam client for 1-2 friends).
Starting yesterday factorio started crashing on some attempts to do the regular 10min autosaves, reverting back and forth trying to load older saves to continue from ...

I'm afraid it isn't. Just had this for the "4" character in my game. A restart fixed it.
Initially it might be related to me switching a second screen on (win+p to extended screen) during the game load screen (the one directly after starting, not loading of a save game).